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United States Patent |
6,059,720
|
Furusawa
,   et al.
|
May 9, 2000
|
Endoscope system with amplification of fluorescent image
Abstract
An endoscope system is provided with an endoscope unit which emits an
excitation light to an object to be observed and receives a fluorescent
light emitted by the object, a filtering optical element, which extracts a
predetermined component of the fluorescent light received by the endoscope
unit, an image capturing device, which receives an image formed by the
predetermined component of the fluorescent light, an amplifier, which
amplifies an output signal of the image capturing device, and a gain
controller, which automatically controls a gain of the amplifier in
accordance with the output signal of the image capturing element.
Inventors:
|
Furusawa; Koichi (Tokyo, JP);
Kaneko; Atsumi (Tokyo, JP)
|
Assignee:
|
Asahi Kogaku Kogyo Kabushiki Kaisha (Tokyo, JP)
|
Appl. No.:
|
035337 |
Filed:
|
March 5, 1998 |
Foreign Application Priority Data
Current U.S. Class: |
600/160; 348/76; 600/109 |
Intern'l Class: |
A61B 001/04 |
Field of Search: |
600/109,160
348/65,76,300
|
References Cited
U.S. Patent Documents
4791480 | Dec., 1988 | Muranaka | 358/65.
|
4951135 | Aug., 1990 | Sasagawa et al. | 348/65.
|
4967269 | Oct., 1990 | Sasagawa et al. | 348/65.
|
5078150 | Jan., 1992 | Hara et al.
| |
5162913 | Nov., 1992 | Chatenever et al. | 358/65.
|
5452723 | Sep., 1995 | Wu et al.
| |
5507287 | Apr., 1996 | Palcic et al.
| |
5701903 | Dec., 1997 | Sano et al.
| |
5749830 | May., 1998 | Kaneko et al. | 600/109.
|
Foreign Patent Documents |
6-54792 | Mar., 1994 | JP.
| |
7155292 | Jun., 1995 | JP.
| |
7204156 | Aug., 1995 | JP.
| |
7-77580 | Aug., 1995 | JP.
| |
8224210 | Sep., 1996 | JP.
| |
Primary Examiner: Leubecker; John P.
Attorney, Agent or Firm: Greenblum & Bernstein, P.L.C.
Claims
What is claimed is:
1. An endoscope system for observing a fluorescent image, comprising:
an endoscope unit which emits an excitation light to an object to be
observed and receives a fluorescent light emitted by said object;
a filtering optical element, which extracts a predetermined color component
of said fluorescent light received by said endoscope unit;
an image capturing device, which receives an image formed by said
predetermined color component of said fluorescent light and outputs an
image signal;
a variable gain amplifier, a gain of which changes in accordance with said
image signal output by said image capturing device;
said variable gain amplifier comparing said image signal output by said
image capturing device with a plurality of reference values defining a
plurality of signal level ranges;
said gain of said variable gain amplifier being changed stepwisely in
accordance with a signal level range in which said image signal is
included;
said variable gain amplifier comprising a first amplifying circuit which
amplifies said output signal of said image capturing device and outputs a
first output signal, said first output signal fluctuating with respect to
a predetermined value;
a second amplifying circuit which amplifies said first output signal at a
predetermined gain and outputs a second output signal;
a first circuit which prepares said first output signal with a first higher
reference value which is higher than said predetermined value, said first
circuit lowering said gain of said second amplifying circuit if said first
output signal has a higher value than said first higher reference value;
and
a second circuit which compares said first output signal with a first lower
reference value which is lower than said predetermined value, said second
circuit lowering said gain of said second amplifying circuit if said first
output signal has a lower value than said first lower reference value.
2. The endoscope system according to claim 1, wherein said variable gain
amplifier further comprises:
a third circuit which compares said first output signal with a second
higher reference value which is higher than said first higher reference
value, said third circuit further lowering said gain of said second
amplifying circuit if said first output signal has a higher value than
said second higher reference value; and
a fourth circuit which compares said first output signal with a second
lower reference value which is lower than said first lower reference
value, said fourth circuit lowering said gain of said second amplifying
circuit if said first output signal has a lower value than said second
lower reference value.
3. The endoscope system according to claim 1, wherein said predetermined
component is a light having a wavelength within a range of 500 nm through
570 nm.
4. The endoscope system according to claim 1, further comprising a display
device which displays said image of a fluorescing object.
5. The endoscope system according to claim 1, further comprising an image
intensifier provided in front of said image capturing device which
amplifies an intensity of received light.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an endoscope system for observing a
fluorescing object, and more particularly to an endoscope system which
emits excitation light towards an object to be observed, receives a
fluorescent light emitted by the object, and display an image of the
fluorescing object.
It has been known that, when organic tissues are illuminated by light
having wavelengths of 420 nm through 480 nm, fluorescent substances
included in the organic tissues such as NAHD, FMN fluoresce. By observing
an image of the fluorescing organic tissues, a disorder of the organic
tissue can be found. Specifically, light fluoresced by normal (i.e., not
diseased) organic tissues includes more green component than a red
component, while light fluoresced by organic tissues having a disorder
includes less green component than the red component. Thus, based on the
amount of the green fluorescent light, whether the organic tissues has a
disorder can be determined.
The amount of the fluorescent light, however, varies depending on a
distance between the organic tissue and a distal end of the endoscope. For
example, if the distal end of the endoscope is relatively close to organic
tissues having a disorder, the amount of the fluorescent light may be as
much as that of organic tissues which do not have a disorder.
In order to avoid such a deficiency, in an endoscope utilizing the
fluorescent light, diagnosis may be done based on a ratio of the green
component of the fluorescent light to the red component.
In order to obtain the ratio of the green component to the red component,
however, an imaging unit is required to include color filters for
separating the red and green components from the fluorescent light, a pair
of image intensifiers for the red and green components, and a pair of CCDs
(Charge Coupled Devices) for the red and green components. Due to such a
structure, the imaging unit becomes relatively large in size, and heavy,
which lowers an operability of the endoscope. Further, due to a large
number of elements, the endoscope utilizing the fluorescent light tends to
be expensive.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improved endoscope
system utilizing the fluorescent light which enables accurate diagnosis
regardless of the distance between the object (e.g., the organic tissues)
and the distal end of the endoscope, and further the imaging unit thereof
can be made compact.
For the object, according to the invention, there is provided an endoscope
system for observing an image of a fluorescing object, comprising: an
endoscope unit which emits an excitation light to an object to be observed
and receives a fluorescent light emitted by the object; a filtering
optical element, which extracts a predetermined component of the
fluorescent light received by the endoscope unit; an image capturing
device, which receives an image formed by the predetermined component of
the fluorescent light; an amplifier, which amplifies an output signal of
the image capturing device; and a gain controller, which automatically
controls a gain of the amplifier in accordance with the output signal of
the image capturing element.
Since the gain of the amplifier is controlled based on the image signal
output by the image capturing device, an appropriate signal can be
obtained even though the distance between the distal end of the endoscope
and the organic tissues to be observed is not appropriate, and/or the
light illuminating the object is not appropriate.
In particular, the gain controller increases the gain of the amplifier when
the output of the image capturing device is within a predetermined value
range.
Optionally or alternatively, it is preferable that the gain controller
decreases the gain of the amplifier when the output of the image capturing
device is out of a predetermined value range.
Further, the endoscope system may be provided with a discriminating system
which determines one of a plurality of value ranges in which the output of
the image capturing is included, and wherein the gain controller
determines the gain of the amplifier based on a value range is which the
output of the image capturing included.
Still optionally, the predetermined component may be a light having a
wavelength within a range of 500 nm through 570 nm.
According to another aspect of the invention, there is provided an
endoscope system for observing an image of a fluorescing object,
comprising: an endoscope unit which emits an excitation light to an object
to be observed and receives a fluorescent light emitted by the object; a
filtering optical element, which extracts a predetermined component of the
fluorescent light received by the endoscope unit; an image intensifier
which amplifies an intensity of a received light; an image capturing
device, which receives an image formed by the predetermined component of
the fluorescent light, the image intensifier being provided in front of
the image capturing device; a driver which controls a gain of the image
intensifier; and controller, which controls a gain of the image
intensifier in accordance with the output signal of the image capturing
device.
Optionally, the driver changes gain of the image intensifier by changing a
voltage applied to the image intensifier.
In this case, the controller controls the driver to decrease the voltage
when output of the image capturing device outputs a signal having a value
within a predetermined value range.
Further, the controller controls the driver to increase the voltage when
output of the image capturing device outputs a signal having a value out
of a predetermined value range.
Optionally, the controller controls the gain of the image intensifier based
on a peak value of output signal of the image capturing device within a
predetermined period.
Still optionally, the gain controller changes the gain of the image
intensifier only when the peak value of the output signal is greater than
a predetermined reference peak value.
Furthermore, the predetermined period corresponds to a period in which the
image capturing device output the signal for one frame.
According to further aspect of the invention, there is provided an
endoscope system for observing a fluorescent image, comprising: an
endoscope unit which emits an excitation light to an object to be observed
and receives a fluorescent light emitted by the object; a filtering
optical element, which extracts a predetermined color component of the
fluorescent light received by the endoscope unit; an image capturing
device, which receives an image formed by the predetermined color
component of the fluorescent light and outputs an image signal; and a
variable gain amplifier, a gain of which changes in accordance with the
image signal output by the image capturing device.
Optionally, the variable gain amplifier may compare the image signal output
by the image capturing device with a plurality of reference values
defining a plurality of signal level ranges, and wherein the gain of the
variable gain amplifier is changed stepwisely in accordance with a signal
level range in which the image signal is included.
In particular, the variable gain amplifier may include: a first amplifying
circuit which amplifies the output signal of the image capturing device
and outputs a first output signal, the first output signal fluctuates with
respect to a predetermined value; a second amplifying circuit which
amplifies the first output signal at a predetermined gain and outputs a
second output signal; a first circuit which compares the first output
signal with a first higher reference value which is higher than the
predetermined value, the first circuit lowering the gain of the second
amplifying circuit if the first output signal has a higher value than the
first higher reference value; a second circuit which compares the first
output signal with a first lower reference value which is lower than the
predetermined value, the second circuit lowering the gain of the second
amplifying circuit if the first output signal has a lower value than the
first lower reference value.
Further optionally, the variable gain amplifier further may include: a
third circuit which compares the first output signal with a second higher
reference value which is higher than the first higher reference value, the
third circuit further lowering the gain of the second amplifying circuit
if the first output signal has a higher value than the second higher
reference value; and a fourth circuit which compares the first output
signal with a second lower reference value which is lower than the first
lower reference value, the fourth circuit lowering the gain of the second
amplifying circuit if the first output signal has a lower value than the
second lower reference value.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic structure of an endoscope system according to a
first embodiment of the invention;
FIG. 2 schematically shows a structure of an image intensifier employed in
the endoscope system shown in FIG. 1;
FIG. 3 a block diagram of a CCD camera unit used in the endoscope shown in
FIG. 1;
FIG. 4 (which consists of FIGS. 4A and 4B) shows a circuitry of the CCD
camera unit shown in FIG. 3;
FIGS. 5A and 5B show wavelength of an output signal of the CCD shown in
FIG. 3;
FIG. 6 shows I/O characteristics of an amplifier when gain control is
performed;
FIG. 7 shows a schematic structure of an endoscope system according to a
second embodiment of the invention;
FIG. 8 schematically shows a structure of an image intensifier and a CCD
camera unit according to the second embodiment; and
FIG. 9 shows a configuration of the image intensifier control circuit shown
in FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a structure of an endoscope system 100 according to a first
embodiment of the invention. The endoscope system 100 includes an
endoscope 10, a light source unit 20 which emits light for illuminating an
object to be observed, and an imaging unit 30 for capturing image of the
object. A display device 50 is connected to the imaging unit 30 via a
video switching device 40.
As shown in FIG. 1, the endoscope 10 has insertion portion 11 having a
cylindrical shape, an operation portion 12 which is connected to a
proximal end of the insertion portion 11, and a light guide connecting
tube 13 which is formed as an extension of the outer surface of the
operation portion 12. The operation portion 12 is provided with an
eyepiece unit 12a by which the endoscope 10 and the imaging unit 30 are
detatchably connected. At a distal end of the light guide connecting tube
13, a connector 13a is provided. The endoscope 10 is detatchably connected
to the light source unit 20 by means of the connector 13a.
As shown in FIG. 1, an image guide fiber bundle 14 is enclosed, in the
endoscope 10, from the distal end of the insertion portion 11 to the
proximal end of the operation portion 12. Inside the distal end of the
insertion portion 11, an objective optical system 15 which forms an image
of the object on a light receiving end surface of the image guide fiber
bundle 14 is accommodated. On the side end of the insertion portion 11 at
a position corresponding to the objective optical system 15, a window 18
is formed to introduce light from the object towards the objective optical
system 15.
In the eyepiece unit 12a, an eyepiece lens 16 is accommodated for observing
the image which is guided from the light receiving end surface to a light
emerging end surface of the image guide fiber bundle 14. It should be
noted that the eyepiece lens 16 is usually used such that an observer can
view the image therethrough. However, if the imaging unit 30 is connected
as shown in FIG. 1, the eyepiece lens 16 is moved to a position
corresponding to 0 (zero) diopter. The light emitted by the object located
in front of the distal end of the endoscope 10 is introduced inside the
endoscope 10, and converged by the objective optical system 15. The image
formed by the objective optical system 15 is transmitted by the image
guide fiber bundle 14 towards the eyepiece unit 12a, and then introduced
to the imaging unit 30 through the eyepiece lens 16.
Inside the endoscope 10, from the end of the connector 13a to the distal
end of the insertion portion 11, a light guide fiber bundle 17 is
provided. A light receiving surface (i.e., a connector 13a side surface)
of the light guide fiber bundle 17 faces the light source unit 20 when the
connector 13a is connected to the light source unit 20. An light emerging
surface (i.e., a distal end side surface) of the light guide fiber bundle
17 is arranged perpendicular to an optical axis of the objective optical
system 17. In front of the light guide fiber bundle 17, on the end surface
of the endoscope 10, a window 19 is formed.
Inside the light source unit 20, a Xenon lamp 21 is provided at a position
opposing to the light guide fiber bundle 17 when the connector 13a is
connected to the light source unit 20. When the Xenon lamp 21 emits light,
the light is converged and incident on the light receiving surface of the
light guide fiber bundle 17. The light is then transmitted inside the
light guide fiber bundle 17 and emerged from the other end of the light
guide fiber bundle 17, and emitted outside through the window 19.
A filter 22 for excitation light is movably provided such that the filter
22 can be inserted in or retracted from an optical path between the lamp
21 and the light receiving surface of the light guide fiber bundle 17, by
means of a solenoid (not shown). The filter 22 is inserted in the optical
path when the fluorescent image is to be observed, and is retracted from
the optical path when a normal image is observed. The filter 22 allows
light having a wavelength within a range of 420 nm through 480 nm. The
organic tissues, when illuminated with the excitation light having the
wavelength of 420 nm through 480 nm, fluoresce and emit light. Normal
organic tissues (which do not have disorder) fluoresce and emit light
having a wavelength within a range of 500 nm through 570 nm. The
fluorescent light emitted by the organic tissues pass through the
observing window 18, the objective optical system 15, and incident on the
light receiving surface of the image guide fiber bundle 14.
The imaging unit 30 accommodates an imaging optical system 30a which
constitutes, together with the eyepiece lens 16, a relay optical system.
At a position where the imaging optical system 30a forms an image, a CCD
camera 31 for normal observation is disposed. Further, as shown in FIG. 1,
another CCD camera 41 for observing fluorescent light image is disposed
next to the CCD camera 31. In this embodiment, the CCD camera 31 and the
CCD camera 41 have the same structure. The CCD cameras 31 and 41 are
connected to a switching device 40 which is connected to the display
device 50. The switching device 40 transmits one of the signals output by
the CCD camera 31 and CCD camera 41 to the display device 50.
Between the CCD camera 31 and the eyepiece lens 16, a mirror 32 which is
retractably inserted in the optical path between the eyepiece lens 16 and
the CCD camera 31 is provided. The mirror 32 deflects the light emerged
from the eyepiece lens 16 when inserted within the optical path. When the
normal observation is performed, the mirror 32 is retracted from the
optical path as indicated by a solid line in FIG. 1. When the fluorescent
image is to be observed, the mirror 32 is inserted in the optical path. In
this case, the optical axis of the eyepiece lens 16 intersects the
reflection surface of the mirror 32 at 45 degrees as indicated by broken
lines in FIG. 1 such that light emerged from the eyepiece lens 16 is
deflected at 90 degrees.
On the optical axis of the eyepiece lens 16 deflected by the mirror 32, a
dichroic mirror 33 is provided such that the optical axis intersects the
reflection surface of the dichroic mirror 33 at 45 degrees. The dichroic
mirror 33 reflect light having a wavelength within a range of 500 nm
through 570 nm, and allows the other light to pass through.
On the optical path of the light reflected by the dichroic mirror 33, an
imaging optical system 33a is provided, and at a position where an image
is formed by the imaging optical system 33a, an image intensifier 34 for
amplifying an intensity of light reflected by the dichroic mirror 33 is
provided. It should be noted that an optical path length between the
eyepiece lens 16 and the CCD camera 31 and an optical path length between
the eyepiece lens 16 and the image intensifier 34 are the same.
FIG. 2 schematically shows a structure of the image intensifier 34. In FIG.
2, the image intensifier 34 includes a first fiber plate 35 having a
photo-electrical surface 35a, a micro channel plate (MCP) 36, and a second
fiber plate 37 which has a fluorescent surface 37a. When an image of the
organic tissues is formed on the first fiber plate 35 by the imaging
optical system 33a, the first fiber plate 35 divides the formed image into
pixels and transmits the pixels, and transmits the light to the
photo-electrical surface 35a. The photo-electric surface 35a thus converts
the optical image into an electronic image. On both sides of the MCP 36,
electrodes are connected to which a predetermined voltage is applied.
Thus, the electronic image converted by the photo-electric surface 35a is
amplified when passes through the MCP 36, and is projected on the
fluorescent surface 37a at which the electronic image is converted into an
optical image. The converted optical image is transmitted to an opposite
side surface of the second fiber plate 37. As above, the fluorescent
object image amplified by the image intensifier 34 is relayed by the
imaging optical system 39 provided on the light emerging surface side of
the image intensifier 34, and is incident on the CCD camera 41 for
observing the fluorescent image.
FIG. 3 is a block diagram illustrating the CCD camera 41. As shown in FIG.
3, the CCD camera 41 includes a CCD (Charge Coupled Device) 51, an
amplifier 53 for amplifying an output signal of the CCD 51, an automatic
gain controller (AGC) 54 which controls a gain of the amplifier 53, and a
video signal conversion circuit 55 for converting the output signal of the
amplifier 53 into a video signal.
CCD 51 is an area sensor for receiving the image output from the light
emerging surface of the image guide fiber bundle 14. The CCD 51 is
arranged such that the light receiving surface of the CCD 51 is
substantially perpendicular to the optical axis of the imaging optical
system 39. The output signal of the CCD 51 is input to the amplifier 53
and the AGC 54.
The amplifier 53 amplifies the signal output by the CCD 51 at a certain
gain, the transmits the amplified signal to the video signal conversion
circuit 55. In this embodiment, the gain of the amplifier 53 is variable,
and is controlled by the AGC 54.
The AGC 54 controls the gain of the amplifier 53 based on the amplitude of
the CCD 51 so that the output signal of the amplifier 53 has a value
within a predetermined range. That is, if the amplitude of the signal
supplied from the CCD 51 to the AGC 54 is greater than a predetermined
reference value (e.g., if a distance between the distal end of the
endoscope 10 and the object to be observed is shorter than an appropriate
distance, or intensity of excitation light illuminating the object is
larger than an appropriate amount), the AGC 54 lowers the gain of the
amplifier 53. On the other hand, if the amplitude of the signal supplied
from the CCD 51 to the AGC 54 is less than the predetermined reference
value (e.g., if a distance between the distal end of the endoscope 10 and
the object to be observed is greater than the appropriate distance, or
intensity of excitation light illuminating the object is less than the
appropriate amount), the AGC 54 increases the gain of the amplifier 53.
The video signal conversation circuit 55 receives the output signal of the
amplifier 53 and converts the received signal into the video signal (e.g.,
an NTSC signal), and transmits the converted signal to the switching
device 40.
FIGS. 4A and 4B shows a circuitry of the CCD camera 41.
An output terminal of the CCD 41 is connected, through a resistor R10 to an
inverting input terminal of the operational amplifier U1B. A non-inverting
input terminal of the operational amplifier U1B is connected, through a
resistor R14 and a variable resistor R17, to a voltage source Vcc. A feed
back resistor R9 connects the output terminal and the inverting input
terminal of the operational amplifier U1B. Further, the output terminal of
the operation amplifier U1B is connected with a condenser C1 for
preventing a DC component from being transmitted. The other end of the
condenser C1 is connected to a resistor R16 for discharging the condenser
C1. With this construction, a DC (direct current) component of the output
signal of the CCD 51 is removed by the condenser C1.
The end of the condenser C1 at which the resistor R16 is connected, is also
connected, through a resister R11, to the inverting input terminal of an
operational amplifier U2B. The non-inverting input terminal of the
operational amplifier U2B is connected to an end of a resistor R15, the
other end of which is grounded. A feed back resistor R7 connects the
output terminal and the inverting input terminal of the operational
amplifier U2B. The output of the operational amplifier U2B is input to the
video signal conversion circuit 55.
An example of change of the output voltage of the CCD 51 (i.e., a voltage
applied to the inverting input terminal of the operational amplifier U1B)
is shown in FIG. 5A. The output voltage is lowered, with respect to a
predetermined voltage, i.e., Vcc, in accordance with amount of light
received by the CCD 51. The output voltage of the CCD 51 is inverted and
amplified by the operational amplifier U1B, and output thereby. The output
voltage of the operational amplifier U1B is applied, through the condenser
C1, at a point X in FIG. 4A, and an example thereof, which corresponds to
the output voltage of the CCD 51 shown in FIG. 5A is indicated in FIG. 5B.
The voltage at the point X is inverted and amplified by the operational
amplifier U2B, the output voltage of which is applied to the video signal
conversation circuit 55.
If the output voltage of the operational amplifier U2B is less than a first
predetermined negative reference value, an output value control circuit
54A, which is indicated by one-dotted lines in FIG. 4A, functions to
substantially lower the gain of the operational amplifier U2B. The output
value control circuit 54A is described in detail hereinafter.
The point X is connected to the inverting input terminal of the operational
amplifier U1A. The inverting input terminal of the operational amplifier
U1A is also connected with a resistor R2 and a variable resistor R1 which
is connected to a constant voltage source. The non-inverting input
terminal of the operational amplifier U1A is connected to a resistor R8
the other end of which is grounded. Between the output terminal and the
inverting input terminal of the operational amplifier U1A, a diode D1 is
connected. Further, to the output terminal of the operational amplifier
U1A, a diode D2, a resistor R5, and a resistor R6 are connected in series.
The end of the resistor R6 is connected to resistor R7 and the inverting
input terminal of the operational amplifier U2B. At a point where the
resistor R2 is connected to the inverting input terminal of the
operational amplifier U1A, an end of the resistor R3 is connected, the
other end of the resistor R3 is connected to the diode D2 and a source of
an FET Q1. A gate of the FET Q1 is connected to the output terminal of a
comparator 541B. The source of the FET Q1 is connected to a connecting
point Y1 of the resistor R5 and the diode D2, and a drain of the FET Q1 is
connected to the other end of the resistor R5. It should be noted that the
FET Q1 is turned On or OFF by the comparator 541B which will be described
in detail.
With this construction, the output voltage of the output voltage control
circuit 54A is 0 (zero) volt when the voltage output by the operational
amplifier U1B is negative. To the resistor R2, a negative reference
voltage VR2 is applied. Therefore, if the absolute value of the voltage (a
positive voltage Vin at the point X) applied to the resistor R2 is smaller
than the negative reference voltage VR2, the diode D1 is forward-biased
and the diode D2 is reverse-biased, and accordingly the operational
amplifier U1A does not amplify the input voltage. If the absolute value of
the positive voltage Vin is greater than the absolute value of the
negative reference voltage VR2, the diode D1 is reverse-biased, and
accordingly an electrical current flows across the resistors R3 and R4. In
this case, the operational amplifier U1A invert-amplifies the input
voltage applied to the inverting input terminal at a predetermined gain.
It should be noted that, by changing the value of the variable resistor R1
to change the voltage VR2, the characteristic of the output value control
circuit 54A can be changed.
Similar to the above, if the output voltage of the operational amplifier
U2B is greater than a first positive reference value, an output value
control circuit 54B, which is indicated by two-dotted lines in FIG. 4A,
functions to substantially lower the gain of the operational amplifier
U2B. The output value control circuit 54B is now described in detail
hereinafter.
The point X is connected to the inverting input terminal of the operational
amplifier U2A through a resister R12. The inverting input terminal of the
operational amplifier U2A is also connected with a resistor R18 and a
variable resistor R21 which is connected to a positive constant voltage
source. The non-inverting input terminal of the operational amplifier U2A
is connected to a resistor R22 the other end of which is grounded. Between
the output terminal and the inverting input terminal of the operational
amplifier U2A, a diode D3 is connected. Further, to the output terminal of
the operational amplifier U2A, a diode D4, a resister R19, and a resister
R20 are connected in series. The end of the resistor R20 is connected to
resistor R7 and the inverting input terminal of the operational amplifier
U2B. At a point where the resistor R18 is connected to the inverting input
terminal of the operational amplifier U2A, an end of the resistor R13 is
connected, the other end of the resistor R13 is connected to the diode D4
and a source of an FET Q2. A gate of the FET Q2 is connected to the output
terminal of a comparator 542B. The source of the FET Q2 is connected to a
connecting point Y2 of the resistor R19 and the diode D4, and a drain of
the FET Q2 is connected to the other end of the resistor R19. It should be
noted that the FET Q2 is turned ON or OFF by the comparator 542B which
will be described in detail.
With this construction, the output voltage of the output voltage control
circuit 54B is 0 (zero) V when the voltage output by the operational
amplifier U1B is positive. To the resistor R18, a positive reference
voltage VR18 is applied. Therefore, if the voltage Vin at the point X is
negative and the absolute value of the voltage Vin is smaller than the
positive reference voltage VR18, the diode D3 is forward-biased and the
diode D4 is reverse-biased, and accordingly the operational amplifier U2A
does not amplify the input voltage. If the absolute value of the negative
voltage Vin is greater than the absolute value of the positive reference
voltage VR18, the diode D3 is reverse-biased, and accordingly an
electrical current flows across the resistors R18 and R13. In this case,
the operational amplifier U2A invert-amplifies the input voltage applied
to the inverting input terminal at a predetermined gain. It should be
noted that, by changing the value of the variable resistor R21 to change
the voltage VR18, the characteristic of the output value control circuit
54B can be changed.
In the circuitry shown in FIGS. 4A and 4B, a voltage Vc at the output
terminal C of the operational amplifier U2B is expressed as follows.
Vc=-(Vc1+Vc2+Vc3) (1)
In equation (1), voltage Vc1 represents an output voltage of the
operational amplifier U2B based only on the output voltage of the
operational amplifier U1A, and is expressed as follows:
Vc1=-Vy1.times.(R7/R5+R6)) (2),
where Vy1 is a voltage at the point Y1.
In equation (1), voltage Vc2 is an output voltage of the operational
amplifier U2B based only on the output voltage of the operational
amplifier U1B, and is expressed as follows:
Vc2=-Vx.times.(R7/R11) (3),
where Vx is the voltage at the point X (i.e., Vx=Vin).
In equation (1), voltage Vc3 is an output voltage of the operational
amplifier U2B based only on the output voltage of the operational
amplifier U2A, and is expressed as follows:
Vc3=-Vy2.times.(R7/R19+R20)) (4),
where Vy2 is a voltage at the point Y2.
Accordingly, the operational amplifier U1A varies a negative electrical
current .alpha. (indicated in FIG. 4A) so that the voltage applied to the
inverting input terminal of the operational amplifier U2B to vary.
Similarly, the operational amplifier U2A varies a positive electrical
current .beta. (indicated in FIG. 4A) so that the voltage applied to the
inverting input terminal of the operational amplifier U2B to vary.
The AGC 54 further includes, as shown in FIG. 4B, a first peak hold circuit
541A, the first comparator 541B, a second peak hold circuit 542A, and the
second comparator 542B.
The first peak hold circuit 541A holds the positive peak value of the
voltage Vx of the point X. The first comparator 541B compares the positive
peak value of the point X with a predetermined positive reference voltage,
and if the positive peak value of the point X exceeds a second positive
reference voltage, the first comparator 541B turns on the FET Q1. Then,
the resistor R5 is short-circuited. That is, R5 can be removed from
equation (2), and therefore, the voltage Vc1 in equation (1) will be
expressed as follows.
Vc1=-Vy1.times.(R7/R6) (5)
Therefore, the absolute value of the voltage Vc1 is increased, and
accordingly the current .alpha. is increased. As a result, the output
voltage Vc of the operational amplifier U2B is decreased.
Similar to the above, the second peak hold circuit 542A holds the negative
peak value of the voltage Vx of the point X. The second comparator 542B
compares the negative peak value of the point X with a second negative
reference voltage, and if the negative peak value of the point X becomes
less than the negative reference voltage, the second comparator 542B turns
on the FET Q2. Then, the resistor R19 is short-circuited. That is, R19 can
be removed from equation (4), and the voltage Vc3 is expressed as follows.
Vc3=-Vy2.times.(R7/R20) (6)
Therefore, the absolute value of the voltage Vc3 is increased, and
accordingly the current .beta. is increased. As a result, the output
voltage Vc of the operational amplifier U2B is decreased.
In summary, when the voltage Vx at the point X is within a predetermined
range (which is defined by the first positive reference voltage and the
second positive reference voltage), the output voltage Vc is equal to Vc2
since voltage Vc1 and Vc2 are both zero. If the voltage Vx exceeds the
range defined by the first negative reference voltage and the first
positive reference voltage, but greater than the second negative reference
voltage or less than the second positive reference voltage described
above, the output voltage Vc is expressed by equation (1), and at this
stage voltages Vc1, Vc2 and Vc3 are respectively expressed by equations
(2), (3) and (4). Further, if the voltage Vx becomes greater than the
second positive reference value, or less than the second negative
reference value, the output voltage Vc is expressed by equation (1), and
in this case, voltage Vc1, Vc2 and Vc3 are expressed by equations (5), (3)
and (6), respectively. Therefore, the gain of the amplifier 53 varies in
accordance with the voltage Vx which changes proportional to the change of
the output voltage of the CCD 51.
It should be noted that the period of time during which the peak hold
circuit 541A holds the peak value of voltage Vx corresponds to time
constants determined by the resistor R25 and the condenser C2. Similarly,
the period of time during which the peak hold circuit 542A holds the peak
value of voltage Vx corresponds to time constants determined by the
resistor R29 and the condenser C3. In this embodiment, both of the time
constants are set to 1/30 seconds, which corresponds to one image frame
period. The time constants can be changed by changing values of the
resistors and condensers.
Further, in this embodiment, reference voltages for each of the circuits
53, 53b, 541B, and 542B can be changed. Accordingly, the characteristics
of the gain of the amplifier 53 as shown in FIG. 6 can be arbitrarily set.
FIG. 6 shows an example of an I/O (Input/Output) characteristic of the
amplifier 53 when the gain thereof is controlled by the AGC 54. The CCD 51
outputs voltage which varies either a negative or a positive side with
respect to zero volt. As shown in FIG. 6, when the input voltage is within
a range A (i.e., when the absolute value of the input voltage is
relatively small), the gain of the amplifier 53 is relatively great, while
when the input voltage is out of the range A, and in a range B or C (i.e.,
when the absolute value of the input voltage is relatively great), the
gain of the amplifier 53 is lowered. Further, when the input voltage is in
a range D or E, the gain of the amplifier 53 is much lower. In this
example, there are five ranges of input voltage, and the gain of the
amplifier 53 corresponding to the ranges B and C are substantially the
same, and the gain of the amplifier 53 corresponding to the ranges D and E
are substantially the same. It may be possible to use a different number
of input voltage ranges, and various gains corresponding to the respective
ranges.
For example, in the output voltage control circuit 54A shown in FIG. 4A, by
changing the voltage VR2, the input voltage at which the output voltage
control circuit 54A starts to operate (which is represented by point M1 in
FIG. 6) can be changed. Similarly, in the output voltage control circuit
54B, by changing the voltage VR18, the input voltage at which the output
voltage control circuit 54B starts to operate (which is represented by
point M2 in FIG. 6) can be changed. Further, in the first comparator 541B,
by changing the reference voltage applied to the non-inverting terminal of
the operational amplifier U4A, the peak value of the voltage Vin at which
the FET Q1 is switched between ON and OFF (which is represented by point
M3 in FIG. 6) can be changed. Similarly, in the first comparator 542B, by
changing the reference voltage applied to the non-inverting terminal of
the operational amplifier U4B, the peak value of the voltage Vin at which
the FET Q2 is switched between ON and OFF (which is represented by point
M4 in FIG. 6) can be changed.
Operation of the endoscope system according to the first embodiment will be
described.
Firstly, the insertion portion 11 of the endoscope 10 is inserted in a
human cavity, and the distal end of the insertion portion 11 is located
closely adjacent to an object to be observed.
When a normal image is observed, the filter 22 is retracted from the
optical path, and the mirror 32 is also retracted from the optical path.
The lamp 21 emits a white light, which is directed through the light guide
fiber bundle 17 and the window 19, and is projected on the object, i.e.,
the organic tissues. The organic tissues reflect the light which is
incident, through the window 18, on the objective optical system 15. The
objective optical system 15 converges the reflected light to form an image
which is guided through the image guide fiber bundle 14 and the eyepiece
lens 16 and directed to the imaging unit 30. Then, via the eyepiece lens
16 and the imaging lens 30a, an image of the object is formed on the light
receiving surface of the CCD camera 31. The CCD camera 31 captures the
image, and outputs a video signal which is transmitted to the display
device 50 through the switching device 40.
When the fluorescent image is observed, the filter 22 and the mirror 32 are
inserted in the optical paths. The white light emitted by the lamp 21
passes through the filter 22, and accordingly only the excitation light is
transmitted by the light guide fiber bundle 13 and emitted to the object
through the window 19. The object (i.e., the organic tissues) fluoresces
when the excitation light is projected. The fluorescent light emitted by
the organic tissues is directed through the window 18, to the objective
optical system 15 and converged thereby. The light is then directed, by
the image guide fiber bundle 14, to the imaging unit 30 through the
eyepiece lens 16.
In the imaging unit 30, the fluorescent light emerged from the eyepiece
lens 16 is reflected by the mirror 32, and a part of the light having a
wavelength within a range of 500 nm through 570 nm is reflected by the
dichroic mirror 33. Thus, on the image receiving surface of the image
intensifier 34, the fluorescent image is formed. The image intensifier 34
amplifies the intensity of light forming the fluorescent image, which is
incident on the CCD camera 41 through the imaging optical system.
The image signal is transmitted from the CCD 51 of the CCD camera 41 to the
amplifier 53 and the AGC 54. As described above, the AGC 54 controls the
gain of the amplifier 53 in accordance with the characteristic shown in
FIG. 6. Therefore, if the distance between the distal end of the insertion
portion 11 and the object is closer to an appropriate distance and/or if
the amount of the excitation light projected to the object is greater than
an appropriate amount, the gain of the amplifier 53 is controlled to
lower. On the other hand, if the distance between the distal end of the
insertion portion 11 and the object is further to an appropriate distance
and/or if the amount of the excitation light projected to the object is
less than an appropriate amount, the gain of the amplifier 53 is
controlled to increase. The fluorescent image signal thus processed is
converted in to the video signal (e.g., the NTSC signal) by the video
signal conversion circuit 55, and supplied to the switching device 40.
The switching device 40 then transmits the video signals received from the
CCD camera 41 to the display device 50 for displaying the fluorescent
image (image formed by the fluorescent light).
Then, an observer can observe the fluorescent image displayed by the
display device 50, and determines whether the objective organic tissues
have a disorder.
FIG. 7 shows a schematic structure of an endoscope system according to a
second embodiment. The difference between the first and second embodiment
is that, the CCD camera 41 of the first embodiment is replaced with a CCD
camera 71, and further a driver 75 is added in the second embodiment. The
other portions of the endoscope system shown in FIG. 7 are the same as
those of the endoscope system shown in FIG. 1.
Specifically, as shown in FIG. 8, the CCD camera 71 includes a CCD 151
which is similar to the CCD 51 of the first embodiment, an image
intensifier control circuit 72, and a video signal conversion circuit 155
which is similar to the video signal conversion circuit 55. It should be
noted that, in this embodiment, the image intensifier control circuit has
a function as an amplifier. The image intensifier control circuit 72
controls the driver 75 to vary the voltage applied to the electrodes of
the MCP 36 in accordance with the output signal of the CCD 151.
FIG. 9 shows a configuration of the image intensifier control circuit 72
shown in FIG. 8.
An amplifier amplifies the output signal of the CCD 151. The DC component
of the signal output by the inverting amplifier 152 is removed by a
condenser C1. The output signal of the amplifier 152 is applied to another
amplifier 153. The amplifier 153 amplifies the signal transmitted through
the condenser C1. At a connecting point X of the condenser C1 and the
amplifier 153, a peak hold circuit 160 is connected. The peak hold circuit
160 holds a positive peak value at the point X and output the same. The
output value of the peak hold circuit 160 is applied to a differential
amplifier 73. In the differential amplifier 73, a reference peak voltage
Vrp applied to a non-inverting input terminal of an operational amplifier
U4A has been adjusted such that the voltage Vrp equals to a peak voltage
Vp at the point X when the distance between the object and the distal end
of the endoscope 10 is appropriate, and the amount of light projected to
the object is also appropriate. With the configuration, if the distance
between the object and the distal end of the endoscope 10 is appropriate
and the amount of light projected to the object is also appropriate, the
output of the differential amplifier 73 is zero. If the distance between
the object and the distal end of the endoscope 10 is too short and/or if
the amount of light projected to the object is too much, the peak voltage
Vp becomes greater than the reference peak voltage Vrp, and accordingly
the differential amplifier 73 outputs a negative voltage. If the distance
between the object and the distal end of the endoscope 10 is too long
and/or if the amount of light projected to the object is insufficient, the
peak voltage Vp becomes less than the reference peak voltage Vrp, and
accordingly the differential amplifier 73 outputs a positive voltage. It
should be noted that the condenser C1 and the resister R25 determines the
time constant of the peak hold circuit 160. In this embodiment, the time
constant corresponds to a period during which the CCD 151 outputs the
signal for one frame.
The A/D converter 74 converts the output voltage of the differential
amplifier 73 into a digital value, which is transmitted to the driver 75.
The driver 75 applies a voltage to the electrodes for the MCP 36 in
accordance with the data transmitted from the A/D converter 74.
Specifically, if the digital data represents the positive voltage, the
driver increases the voltage applied to the MCP 36, and if the digital
data represents the negative voltage, the driver decreases the voltage
applied to the MCP 36. If the digital data represents zero, the driver
holds the currently applying voltage.
As above, according to the embodiments, an appropriate image of the
fluorescing object can be obtained, and further, the size of the imaging
unit can be made compact.
By observing the normal image of the object using the CCD camera 31, and
the fluorescent light image of the object using the CCD camera 41, the
observer can determine the organic tissues having a disorder accurately.
The present disclosure relates to subject matter contained in Japanese
Patent Application No. HEI 09-53622, filed on Mar. 7, 1997, which is
expressly incorporated herein by reference in its entirety.
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